Compound motion rubbing machine

ABSTRACT

A portable sander having an air motor with an output shaft driving an eccentric, parallel shaft on which an inverted cupshaped casing is journaled for eccentric motion about the driving shaft. A pinion gear is fast on the motor housing around the motor shaft and meshes with a larger ring gear fast in the upper end of the casing to rotate the casing about an eccentric axis as it moves about the axis of the driving shaft. The casing carries a rubbing shoe to which a sheet of sandpaper is attached for contact with a work surface.

United States Patent [191 Heffran, Jr.

[ Dec. 31, 1974 COMPOUND MOTION RUBBING MACHINE 211 Appl. No.: 339,164

[52] US. Cl. 5l/170 MT [51] Int. Cl B241) 23/04 [58] Field of Search51/170 MT, 170 R, 170 T,

51/120, 177; 15/22 R, 49 R g [56] References Cited UNITED STATES PATENTS2,178,937 11/1939 'Nieder 51/120 2,740,237 4/1956 Day 3,105,328 10/1963Torres 3,199,251 8/1965 Enders 9/1965 Levegue 51/170 R 11/1966 bevegue51/120 Primary Examiner- Donald G. Kelly Attorney, Agent, or Firm-Wolfe,Hubbard, Leydig, Voit & Osann Ltd.

[ 57] ABSTRACT A portable sander having an air motor with an outputshaft driving an eccentric, parallel shaft on which an invertedcup-shaped casing is journaled for eccentric motion about the drivingshaft. A pinion gear is fast on the motor housing around the motor shaftand meshes with a larger ring gear fast in the upper end of the casingto rotate the casing about an eccentric axis as it moves about the axisof the driving shaft. The casing carries a rubbing shoe to which a sheetof sandpaper is attached for contact with a work surface.

9 Claims, 5 Drawing Figures PATENIED E531 I974 1 COMPOUND MOTION RUBBINGMACHINE BACKGROUND OF THE INVENTION the rolling motion during eccentricmovement of the shoe. A prior machine of this general type is disclosedin U.S. Pat. No. 3,205,622 wherein it will be seen that the ring memberis fixed to the motor housing or frame and the pinion or wheel rollsaround the interior of the ring.

SUMMARY OF THE PRESENT INVENTION The primary object of thepresentinvention is to improve the performance of machines of theforegoing character by a basic structural change making possible themore effective utilization of available power and providing an improvedand more effective compound motion of abrasive particles on the shoerelative to a work surface. More specifically, the invention utilizesthe motion produced by moving the ring member around a stationary wheelmember to obtain epicycloidal motion of the abrasive particles, and thisis believed to be responsible for the more effective rubbing action.

Other objects are to facilitate optimum counterbalancing of the movingparts, to provide a substantial working mass for ruggedness ofconstruction and performance of the machine and to provide a rugged andcomparatively large mounting for the'rubbing shoe.

Other objects and advantages of the invention will become apparent fromthe following detailed description taken in connection with theaccompanying draw.-

ings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view of aportable sander embodying the novel features of the present invention,certain parts of the sander being broken away and shown in section.

FIG. 2 is an enlarged fragmentary cross-sectional view takensubstantially along the line 22 of FIG. 1.

FIG. 3 is a fragmentary cross-sectional view taken along the line 3-3 ofFIG. 2.

FIG. 4 is a view similar to FIG. 3 with the parts in moved positions.

FIG. 5 is an enlarged view schematically illustrating the paths followedby particles on the rubbing shoe during operation of the sander.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT- As shown in thedrawings for purposes of illustration, the invention is embodied in aportable sander l0 powered by a motor in a hollow frame or housing 11beneath which a rubbing shoe I2 is supported for gyratory motion aboutthe axis 13 of the depending motor shaft I4. The lower end portion ofthe motor shaft projects through and is joumaled in an anti-frictionbearing 15 (FIG. 2) fitted in a plate 18 forming the bottom wall of themotor housing. The rubbing shoe is carried by an eccentric indicatedgenerally at 19 on the lower end of the drive shaft.

In the present instance, the sander 10 is powered by a rotary air motorwhich receives air under pressure through a flexible hose 20 connectedto the free end of a handle 21 on the housing 11 and communicating withthe motor through 'an air passage in the handle. The flow of air to themotor is controlled by a lever 22 extending outwardly from the casingalong the top of the handle and movable toward and away from the latterto open and close a valve 23 interposed between the air passage and themotor. The construction and operation of the motor and the control valveare well known to those skilled in the art and thus are not described indetail herein.

As shown in FIG. 2, the eccentric 19 comprises a crank disk 24 securedto the lower end of the drive shaft 14 beneath the bearing 15 with asecond shaft 25 projecting downwardly from the disk in radially offsetparallel relation with the drive shaft. The rubbing shoe 12 is supportedon a carrier 26 joumaled on the eccentric shaft 25 to turn about theaxis 27 of such shaft and to wobble eccentrically about the axis 13 ofthe drive shaft. Herein, the shoe comprises a pad 28 of resilientlyyieldable material secured to the underside of a flat circular backingplate 29 fastened to the carrier in a plane perpendicular to the axes ofthe shafts 14 and 25. A sheet 30 of abrasive material such as sandpaperis fastened to the underside of the pad for rubbing engagement with awork surface.

With the foregoing general arrangement, rotation of the motor shaft 14at high speed, for example, at 4,0006,000 r.p.m., swings the carrier 26about the axis 13 ofthe motor shaft to impart a gyratory or wobblingmotion to the rubbing shoe l2 and to the abrasive particles on the sheet30 of abrasive material fastened to the shoe. The amount of eccentricityof the shaft 25 determines the amount of lateral motion or throw of therubbing shoe during each revolution of the drive shaft. For example, theeccentricity may be one-eighth of an inch. It will be understood bythose skilled in the art, however, that the representative figure givenabove is not critical and will vary according to the size of the machineand the type of the rubbing action desired.

In order to improve the abrasive action obtained with gyratory motionmachines of this type, a secondary turning or rolling motion is impartedto the shoe 12 to rotate the latter about the axis 27 of the eccentricshaft 25 as the shoe gyrates about the drive shaft 14. This secondarymotion prevents the formation of circular grooves in the work surface bythe abrasive particles on the shoe by moving the particles alongnon-circular paths. In addition, the compound motion of the shoe assistsin the automatic removal of the foreign material that tends toaccumulate between and around the abrasive particles and thus unloadsthe abrasive sheet in service use.

In accordance with the present invention, an improved and more effectivecompound motion of the shoe 12 is produced by a positive drivecomprising a circular gear wheel or pinion 3l stationarily mounted onthe machine frame 11 and drivingly engaging a ring gear 32 movable withthe carrier 26, the ring gear being larger than and encircling thestationary pinion gear. During gyration of the carrier and the shoe, thering gear rolls continuously around the periphery of the stationary gearto impart a wobbling rotary motion to the carrier and the shoe andproduce an abrasive action which has been found to be superior to theaction of comparable known machines.

In this instance, the pinion 31 is integral with the underside of theplate 18, the pinion and the plate being formed by conventional powderedmetal techniques. The carrier 26 is an inverted cup-shaped casing havinga cylindrical body 26a abutting against and secured by screws 33 to thebacking plate 29. The top wall 34 of the cup is disposed immediatelybeneath the crank disk 24 and is formed with a central circularopening35 in which an antifriction bearing 36 is fitted. The eccentric shaftextends downwardly through this bearing, there being a counterweight 37fastened to and projecting radially from the lower end portion of theshaft beneath the cup wall 34. Thus, the bearing 36 mounts the cup 26and the shoe l2 rotatably on the eccentric shaft 25 in coaxial relationtherewith.

Extending upwardly from the cup body 26a in loosely telescoping relationwith the pinion 31 is an annular rim 38 in which the ring gear 32 isfixed, both the ring gear and the internal surface 39 of the rim beingcoaxial with the eccentric shaft 25 and the carrier body 26a. The ringgear is sized to mesh with the pinion on one side and to roll around thelatter as the carrier gyrates around the axis 13 of the drive shaftthereby utilizing the gyratory motion of the carrier to produce therotary motion as well. FIGS. 3 and 4 show two extreme positions of thering gear and the carrier relative to the pinion and the drive shaft andthe corresponding position of the eccentric shaft 25.

As shown most clearly in FIGS. 3 and 4, the pinion 31 has fewer teeththan the ring gear 32. The amount of eccentricity of the shaft 25 is afactor in determining the tooth differential and also in determining theproper size differential between the ring gear and the pinion, the gearsizes being correlated with the eccentricity to insure that the ringgear remains in meshing engagement with the pinion during gyration ofthe carrier 26. The specific numbers of teeth determine the ratio of thegearing and are a matter of sound design choice. Herein, the ring gearis shown as having 39 teeth while the stationary gear has 36 teeth.

The superior abrasive action obtained with this construction is believedto be the result of several unique effects of the drive arrangement.First, the rolling motion of the carrier 26 and the shoe 12 is forward,that is, in the same direction as the rotation of the drive shaft 14 andthe gyration of the carrier, as indicated by the arrows in FIG. 5.Moreover, the illustrative sander, with 36 teeth on the pinion and 39teeth on the ring gear, has a lower gear ratio than a similar sanderwith a counter-rotating shoe. The increased power thus available at theshoe makes it possible to operate the sander effectively with greaterrubbing pressures.

In FIG. 5, the general paths followed by four radially spaced abrasiveparticles 40 on the shoe during three successive drive shaft revolutionsare shown to illustrate another advantageous effect of the novel drivearrangement. Each particle travels generally along an epicycloidal path,that is, a path of the type generated by a point on an imaginary circlerolling on the outside of a larger base circle 41. Such a path comprisesa plurality of arcs 42 curving outwardly from a point on the base circleand then back to an angularly spaced point where the next arc of thepath begins. It is believed that such epicycloidal paths produce theoptimum amount of particle travel and abrasive contact with the work perrevolution of the drive shaft 13 and thus result in optimum rubbingefficiency.

While the gears 31 and 32 located adjacent the upper end of the carrier26, there is ample room within the carrier for the counterweight 37which is advantageously positioned directly adjacent the top of the shoe12. The addition of the carrier to the gyrating mass not only increasesthe mass but also raises the center of gravity of the mass into ahorizontal plane well above the plane of the shoe. By virtue of the gearlocation and the hollow carrier, it is possible to locate the center ofgravity of the counterweight in the same horizontal plane as the centerof gravity of i the gyrating mass thereby to provide optimumcounterbalancing of the shoe for smooth and vibration-free operation.Moreover, the carrier is of relatively large diameter as a result ofbeing fixed to the ring gear and thus provides a large, rugged andstable support upon which to mount the shoe 12.

I claim as my invention:

1. In a compound motion rubbing machine, the combination of, a frame, adrive shaft journaled on said frame with one end portion projectingdownwardly therefrom, an eccentric shaft mounted on the projecting endportion of said drive shaft in radially offset parallel relationtherewith, an inverted cup-shaped casing disposed around said eccentricshaft and rotatably mounted thereon for gyratory motion about the axisof said drive shaft as the latter rotates, a pinion gear stationarilymounted on the underside of said frame in coaxial relation with saiddrive shaft, said casing having a coaxial annular rim I looselyencircling said pinion gear, a ring gear larger than said pinion gearfast in said rim and disposed around the pinion gear in meshingengagement with one side of the latter, and a rubbing shoe mounted onthe lower end of said casing for movement therewith in rubbingengagement with a work surface, the amount of eccentricity of saideccentric shaft and the sizes of said gears being correlated to producesimultaneous gyrating and rotating motion of said casing during rotationof said drive shaft and generally epicycloidal motion of abrasiveparticles on said shoe relative to a work surface. v

2. The combination defined in claim 1 further including a counterweightmounted on said eccentric shaft above said shoe and within said casingbelow said gears, the centers of gravity of said counterweight and thegyrating mass including said casing and said shoe being disposedgenerally in a common plane perpendicular to said eccentric shaft.

3. In a compound motion rubbing machine, the combination of, a frame, adrive shaft joumaled on said frame with one end portion projectingdownwardly therefrom, an eccentric on the projecting end portion of saiddrive shaft, a hollow carrier disposed around said eccentric androtatably mounted thereon for eccentric motion with the eccentric aboutthe axis of said drive shaft, a pinion gear stationarily mounted on theunderside of said frame in coaxial relation with said drive shaft, saidcarrier having an annular rim projecting upwardly beyond said eccentricin loosely telescoping relation with said pinion gear, a ring gearlarger than said pinion gear mounted inside said rim and meshing withthe pinion gear to roll around the latter during eccentric motion ofsaid carrier and thereby rotate the carrier about said eccentric, and arubbing shoe fast on the lower end of said carrier for compound motionin rubbing engagement with a work surface.

4. In a compound motion rubbing machine, the combination of, a frame, adrive shaft joumaled on said frame, a second shaft eccentrically carriedby said drive shaft for eccentric motion about the axis thereof duringrotation of the drive shaft, a cup-shaped casing rotatably mounted onsaid second shaft for eccentric motion therewith about said axis andsimultaneous rotation about the axis of said second shaft, a pinion gearstaframe, a second shaft eccentrically carried by said drive shaftforeccentric motion about the axis thereof during rotation of the driveshaft, a gear wheel stationarily mounted on said frame in coaxialrelation with said drive shaft, a ring gear internally larger than theexterior of said gear wheel rotatably mounted on said second shaft incoaxial relation therewith for eccentric motion about said axis, saidring gear being disposed around said gear wheel and in rollingengagement therewith to be turned by the gear wheel during saideccentric motion, and a rubbing shoe carried by said ring gear forsimultaneous eccentric and turning movement relative to said framewhereby points on said shoe move along generally epicycloidal paths.

6. The combination defined in claim 5 in which said ring gear is mountedon a hollow casing having one end portion carrying said ring gear andits opposite end portion connected to said shoe, said casing beingjoumaled on said second shaft.

7. The combination defined in claim 6 in which the center of gravity ofthe mass including said casing, said ring gear and said shoe is in aplane between said shoe and said ring gear, and further including acounterweight mounted on said second shaft within said casing and belowsaid ring gear and having a center of gravity substantially in saidplane.

8. The combination defined in claim 6 in which the end of said casingconnected to said shoe is larger in diameter than said ring gear.

9. In a compound motion rubbing machine, the combination of, a frame, adrive shaft journaled on said frame, an eccentric on said drive shaft, acarrier rotatably mounted on said eccentric for eccentric motion aboutthe axis of said drive shaft during rotation of the latter, a wheelstationarily mounted on said frame in coaxial relation with said driveshaft, a ring internally larger than the exterior of said wheel disposedaround the latter in continuous rolling engagement therewith, said ringbeing mounted on said carrier to rotate the latter as it moveseccentrically around said axis, and a rubbing shoe mounted on saidcarrier for movement therewith in rubbing engagement with a worksurface.

1. In a compound motion rubbing machine, the combination of, a frame, adrive shaft journaled on said frame with one end portion projectingdownwardly therefrom, an eccentric shaft mounted on the projecting endportion of said drive shaft in radially offset parallel relationtherewith, an inverted cup-shaped casing disposed around said eccentricshaft and rotatably mounted thereon for gyratory motion about the axisof said drive shaft as the latter rotates, a pinion gear stationarilymounted on the underside of said frame in coaxial relation with saiddrive shaft, said casing having a coaxial annular rim loosely encirclingsaid pinion gear, a ring gear larger than said pinion gear fast in saidrim and disposed around the pinion gear in meshing engagement with oneside of the latter, and a rubbing shoe mounted on the lower end of saidcasing for movement therewith in rubbing engagement with a work surface,the amount of eccentricity of said eccentric shaft and the sizes of saidgears being correlated to produce simultaneous gyrating and rotatingmotion of said casing during rotation of said drive shaft and generallyepicycloidal motion of abrasive particles on said shoe relative to awork surface.
 2. The combination defined in claim 1 further including acounterweight mounted on said eccentric shaft above said shoe and withinsaid casing below said gears, the centers of gravity of saidcounterweight and the gyrating mass including said casing and said shoebeing disposed generally in a common plane perpendicular to saideccentric shaft.
 3. In a compound motion rubbing machine, thecombination of, a frame, a drive shaft journaled on said frame with oneend portion projecting downwardly therefrom, an eccentric on theprojecting end portion of said drive shaft, a hollow carrier disposedaround said eccentric and rotatably mounted thereon for eccentric motionwith the eccentric about the axis of said drive shaft, a pinion gearstationarily mounted on the underside of said frame in coaxial relationwith said drive shaft, said carrier having an annular rim projectingupwardly beyond said eccentric in loosely telescoping relation with saidpinion gear, a ring gear larger than said pinion gear mounted insidesaid rim and meshing with the pinion gear to roll around the latterduring eccentric motion of said carrier and thereby rotate the carrierabout said eccentric, and a rubbing shoe fast on the lower end of saidcarrier for compound motion in rubbing engagement with a work surface.4. In a compound motion rubbing machine, the combination of, a frame, adrive shaft journaled on said frame, a second shaft eccentricallycarried by said drive shaft for eccentric motion about the axis thereofduring rotation of the drive shaft, a cup-shaped casing rotatablymounted on said second shaft for eccentric motion therewith about saidaxis and simultaneous rotation about the axis of said second shaft, apinion gear stationarily mounted on said frame in coaxial relation withsaid drive shaft, a ring gear internally larger than the exterior ofsaid pinion gear mounted on said casing and disposed around the piniongear for continuous rolling engagement therewith to rotate said casingabout said second shaft during eccentric motion of the casing about saiddrive shaft, and a rubbing shoe carried by said casing for movementtherewith in rubbing engagement with a work surface.
 5. In a compoundmotion rubbing machine, the combination of, a frame, a drive shaftjournaled on said frame, a second shaft eccentrically carried by saiddrive shaft for eccentric motion about the axis thereof during rotationof the drive shaft, a gear wheel stationarily mounted on said frame incoaxial relation with said drive shaft, a ring gear internally largerthan the exterior of said gear wheel rotatably mounted on said secondshaft in coaxial relation therewith for eccentric motion about saidaxis, said ring gear being disposed around said gear wheel and inrolling engagement therewith to be turned by the gear wheel during saideccentric motion, and a rubbing shoe carried by said ring gear forsimultaneous eccentric and turning movement relative to said framewhereby points on said shoe move along generally epicycloidal paths. 6.The combination defined in claim 5 in which said ring gear is mounted ona hollow casing having one end portion carrying said ring gear and itsopposite end portion connected to said shoe, said casing being journaledon said second shaft.
 7. The combination defined in claim 6 in which thecenter of gravity of the mass including said casing, said ring gear andsaid shoe is in a plane between said shoe and said ring gear, andfurther including a counterweight mounted on said second shaft withinsaid casing and below said ring gear and having a center of gravitysubstantially in said plane.
 8. The combination defined in claim 6 inwhich the end of said casing connected to said shoe is larger indiameter than said ring gear.
 9. In a compound motion rubbing machine,the combination of, a frame, a drive shaft journaled on said frame, aneccentric on said drive shaft, a carrier rotatably mounted on saideccentric for eccentric motion about the axis of said drive shaft duringrotation of the latter, a wheel stationarily mounted on said frame incoaxial relation with said drive shaft, a ring internally larger thanthe exterior of said wheel disposed around the latter in continuousrolling engagement therewith, said ring being mounted on said carrier torotate the latter as it moves eccentrically around said axis, and arubbing shoe mounted on said carrier for movement therewith in rubbingengagement with a work surface.